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CORE Block 4 > Protein trafficking: Golgi and beyond > Flashcards

Protein trafficking: Golgi and beyond Flashcards

1
Q

Describe the biosynthetic pathway.

A

This is the secretory pathway. Protein synthesis in ER or lipid and carbo synthesis in golgi. These are altered as they pass through the golgi, and from there are sent to various locations (membrane, lysosome, etc.)

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2
Q

What types of proteins go through secretory (exocytotic) pathway?

A

membrane proteins: surface receptors, transporters, ion channels

soluble proteins: digestive enzymes, peptide hormones, serum proteins, ECM proteins

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3
Q

Which pathway is anterograde movement involved in?

A

Secretory

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4
Q

Which pathway is retrograde movement associated with?

A

endosomal or return

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5
Q

How do proteins on vesicles act like the sign on a bus?

A

There are many buses, but the specific sign (or proteins) tells the bus where to go

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6
Q

What are the three main types of vesicle coats?

A
  • clathrin
  • COPI
  • COPII
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7
Q

What is the first layer of specificity of a vesicle?

A

Its type of coat

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8
Q

What is the normal size of all vesicles?

A

100nm

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9
Q

What are the principle functions of the vesicle coat?

A
  1. helps select the appropriate molecules for transport
  2. assembly of coat proteins into curved, basketlike lattices deforms the membrane patch and thereby molds the forming vesicles.
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10
Q

What direction movement is COPI coated vesicles involved in?

A

retrograde: endosomes to golgi and golgi to ER (movement of intracellular vesicles)

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11
Q

What direction movement are COPII coated vesicles involved in?

A

anterograde: ER to golgi (movement of intracellular vesicles)

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12
Q

What direction movement are clathrin coated vesicles involved in?

A

anterograde: golgi to plasma or plasma to golgi

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13
Q

What is the main molecular component of vesicles?

A

Although they are coated in proteins, they are made from lipids

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14
Q

Describe the structure of clathrin and how it coats vesicles.

A
  • clathrin has three heavy chains and three light chains that form a triskellion
  • many triskellions come together to form a clathrin-coated vesicle (convex hexagons and pentagons, like a soccer ball)
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15
Q

How does clathrin impart specificity to vesicle formation?

A
  • clathrin associates with adaptor proteins to help select cargo and form a vesicle
  • the adaptor proteins help mediate the rearrangement of the lipid membrane to allow it to bud off and form a particle (vesicle)
  • adaptor proteins form a second vesicle layer which clathrin coats
  • adaptor proteins traps various transmembrane proteins, inclduing transmembrane receptors that capture soluble cargo molecules inside the vesicle (cargo receptors)
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16
Q

Which components of a vesicle aid in specificity?

A

Cargo, cargo receptor, adaptor proteins, Rab, snares

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17
Q

Are all vesicle adaptor molecules proteins?

A

No, some can be phospholipids.

  • can have phosphorylation of head group, leading to phosphatidylinositol
  • ionisitol can also be phosphorylated, called phosphatidylinositol phosphate
  • the location of phosphorylation provides more specificity to this adaptor molecule
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18
Q

What extra layer of specificity is introduced to vesicles using PIP as an adaptor molecule?

A

PIP receptors

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19
Q

Where do adaptor molecules get their name?

A

They are different at different parts of the cell, and enzymes can convert them, thus “adapting” them, to different forms depending on where they go

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20
Q

How can we tell an exosome from an endosome?

A

We can look at the type of protein it is coated in as well as the type of adaptor molecule/protein is used.

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21
Q

What is dynamin and how does it function in vesicle formation?

A

It is a protein that regulates how the vesicle pinches off from a membrane. Dynamin is specifically a GTPase which regulates the rate at which vesicles pinch off from the membrane.

22
Q

What would we see in an EM image if there is a mutation dynamin?

A

We would see many vesicles budding from a membrane but none would pinch off and be released.

23
Q

What controls when coat proteins come together to form a vesicle?

A

Coat-specific GTPases

24
Q

Which GTPase helps form clathrin-coated vesicles

A

Arf

25
Q

Which GTPase helps form COPI-coated vesicles?

A

Arf

26
Q

Which GTPase helps form COPII-coated vesicles?

A

Sar1

27
Q

Describe how the adaptor molecule aids in the formation of COPII coated vesicles.

A

The Sar1 G protein is the adaptor protein for COPII.

  • Sar1 is off when it is bound GDP
  • Sar1 binds GTP when it binds its GEF sec12 in the ER membrane
  • Sar1 binding of GTP causes conformational change that exposes hydrophobic region of the adaptor protein so that it inserts into the ER membrane
  • membrane-bound Sar1 interacts with sec23 which recruits sec24, where sec24 is bound to the cargo receptor that brings the cargo in the ER lumen to the membrane.
  • sar1 also then binds on the outside to sec13/31 which forms the outer COPII coat
28
Q

What does the COPII coat consist of?

A

sec23/24 inner coat and sec13/31 outer coat

29
Q

What event causes COPII coat disassembly?

A

When the vesicle buds off from the membrane, Sar1 GTP is hydrolyzed to GDP, causing Sar1 to dissociate from the membrane along with the Sec proteins which composed the COPII coat.

30
Q

In what form does a vesicle move from one cellular compartment to another?

A

In its uncoated form.

31
Q

What is the general role of RAB proteins in vesicle trafficking?

A

To ensure that vesicles only go where they are supposed to go/

32
Q

What type of protein is a RAB protein?

A

A monomeric GTPase (binds GTP)

33
Q

In what form are Rab proteins active?

A

In their GTP-bound state they are active and bound to the membrane of an organelle or transport vesicle.

34
Q

Describe the function of Rab and SNARE proteins in vesicle trafficking.

A
  • the specific Rab-GTP binds a specific Rab effector (receptor) on the target compartment, helping to tether the vesicle to the membrane
  • SNARE proteins (v-snare and t-snare) can now come together and fuse the two membranes together

thus, snare does the fusing, but Rab speeds up the process

35
Q

Describe snare proteins and membrane fusion

A
  • snare proteins have helical domains that twist together to push out water
  • formation of trans-snare complex locks the two membranes together
36
Q

From what regions of the ER do COPII-coated vesicles leave?

A

Exit sites. These sites along the membrane are lacking ribosomes.

37
Q

What marks a protein for exit from the ER through a COPII-coated vesicle?

A

It must have an exit signal as well as the cargo receptor must have an exit signal

38
Q

What is ER quality control?

A

The process by which misfolded proteins are detected

39
Q

What are vesicular tubular clusters?

A

The structures formed when ER-derived vesicles fuse with one another. They are generated continuously and function as transport packages that move cargo from ER to golgi

40
Q

What vesicles return cargo to the ER?

A

COPI-coated

41
Q

Which proteins return to the ER from the vesicular tubular clusters?

A

Proteins that have escaped or are involved in vesicle formation and need to be recylced

42
Q

How is BIP chaperone allowed to return from the golgi to the ER?

A

It has a retrieval sequence, KDEL, which allows it to be carried back by COPI-coated vesicle

43
Q

Describe KDEL-containing protein return and how it works.

A
  • KDEL receptors on cis golgi helps package cargo into COPI-coated retrograde vesicle
  • KDEL receptors are pH sensitive, and has a high affinity for KDEL sequence in acidic conditions of the cis golgi. However, back in the ER, the KDEL receptor has a lower affinity for the sequence where pH is neutral and can therefore let go of the cargo into the lumen
44
Q

List the domains of the golgi

A
  1. cis domain (faces ER)
  2. medial golgi
  3. trans golgi (close to plasma membrane)
45
Q

what are golgi cisternae?

A

flat, membrane enclosed structures making up golgi stacks linked together by tubular connections, forming a single complex

46
Q

What functions occur in cis golgi?

A
  • n-glycosylation
  • modification and sorting of proteins destined for lysosome
47
Q

What functions occur in medial golgi?

A

-sugars on glycoproteins are modified

48
Q

What are the functions of the trans golgi?

A
  • sialic acid and sulfate added to glycoproteins, glycolipids, and proteoglycans
  • final sorting occurs to deliver molecules to the plasma membrane, lysosome, or for secretion
49
Q

List and describe the two models for the organization of the golgi and the transport of proteins from one cisternae to the next.

A
  1. vesicular transport model (forward moving transport vesicles that bud and fuse, bud and fuse)
  2. cisternal maturation model (cisternae mature and move forward and rely on COPI-mediated retrograde movement of proteins back to cisternae)
50
Q

Describe regulated secretion.

A

Unlike constitutive, it requires a signal from the cell to secrete.

  • secretory materials are stored in secretory granules close to the plasma membrane
  • they are secreted after the correct stimulus: hormone release (endocrine cells), digestive enzyme release (pancreatic cells), neurotransmitter release (nerve cells)
  • signal binds receptors on cell surface, causing increase in intracellular Ca2+ which helps fusion of granules with plasma membrane
51
Q

What is a genetic approach to study which proteins are involved in secretion of materials from the cell?

A
  • make mutant genes to encode temperature-sensitive proteins
  • when temp increases, see which proteins are involved in a failure for materials to be secreted

CORE Block 4 (8 decks)

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